#include <iostream>
#include <fstream>


using namespace std;
ifstream fin("operatii.in");
ofstream gout("operatii.out");
int v[1001];

int main()
{

	int n, maxx = 0, s = 0;
	fin >> n;
	for (int i = 1;i <= n;i++)
		fin >> v[i];

	for (int i = 1;i <= n;i++)
	{
		if (v[i] != 0)
		{
			while (v[i] != 0)
			{
				if (v[i] >= maxx)
					maxx = v[i];

				i++;
			}
			s += maxx;
		}
		maxx = 0;
	}
	gout << s;



	return 0;

}